In the art of internal transportation in factories, there are often used so called "self-powered" handling systems which consist of a suspended monorail on which run trolleys powered through an electrical distribution line arranged along the monorail. The trolleys usually have a drive wheel placed above the rail and bucking rollers place below it. Traction of the powered upper wheel on the monorail is generally sufficient for level movement and along slight rises. For inclined sections with relatively steep slopes, there have been proposed lower bucking rollers equipped with a spring-loaded system which pushes the rollers toward the rail so as to increase adherence or traction of the drive wheel on the rail as, for example, described in Italian patent n. 202807 in the name of FATA European Group.
The use of pressurized rollers, in addition to being costly, has the drawback of increasing the space occupied by the trolleys, resulting in a greater size for the entire transportation line. In addition, the solution requires a very accurate setting and regulation of the pressures on the rollers to achieve a comprise between ensuring sufficient adherence of the drive wheel along the steeper rises of the path with the maximum load transportable on the one hand without creating excessive generation of stresses on the structure during level running on the other. Even if the optimal compromise is achieved, the pressing rollers, needed to ensure substantially uniform operation and hence supply the necessary friction for running on the steepest rises, when running on level sections or with slight slopes will generate useless stressing of the mechanical parts of the trolley and increase wear of the rolling gear and the rail.
To obviate this last shortcoming there has been proposed, as described in my copending U.S. patent application Ser. No. 800,321, a system of handling using trolleys with a pressing device which is loaded only in the sloping sections as a result of a thickening thereof in relation to the thickness of the rail in the level sections. This solution, while achieving its ends is, however, still encumbered to a certain degree by the cost of the pressing devices and by their complexity of construction and need for adjustment.
Another drawback is that such lower or bucking rollers dependent on elastic pressure means, allow the trolleys to swing in the direction of travel. This swinging is detrimental in the case of transportation systems where operations are to be performed on the loads being carried. For this reason, there are generally used self-powered trolleys capable of independently negotiating sloping sections when processing is to be performed on the loads moving along the line of transportation.
The general object of the present invention is to obviate the above mentioned drawbacks by providing a transportation system of the self-powered type which allows the trolleys to ascend and descend ramps with relatively steep slopes, is of limited size and complexity and free from swinging and in which the thrust of the drive wheel on the rail is substantially a function of the slope being traversed.